A blood glucose level measuring apparatus, an example of concentration measuring apparatus, employs a popular method for measuring the concentration of glucose contained in blood, the method utilizing oxidation-reduction reaction using oxidoreductase as the catalyst. In using the blood glucose level measuring apparatus, a test instrument for providing an enzyme reaction system is attached to the measuring apparatus, and then blood is supplied to the test instrument for the measurement of the blood glucose level. A widely used test instrument for a blood glucose level measuring apparatus may be a biosensor of capillary type which utilizes capillary action for introducing blood to the enzyme reaction system.
FIGS. 16 and 17 illustrate an example of biosensor which utilizes a capillary system. FIG. 16 is an exploded perspective view of the biosensor 90, whereas FIG. 17 is a sectional view of the biosensor 90 in the assembled state, the section being taken along lines XVII-XVII in FIG. 16.
The biosensor 90 includes a substrate 91 on which a spacer 92 and a cover 93 are laminated to define a capillary 94. The capillary 94 is open at a suction port 94a and at a discharge port 94b formed in the cover 93. The substrate 91 is provided with an operative electrode 95, a counterpart electrode 96 and a reagent portion 97. The reagent portion 97 contains oxidoreductase and an electron carrier.
For measuring the blood glucose level using the biosensor 90, blood is introduced via the suction port 94a of the biosensor 90, which is pre-mounted to the blood glucose level measuring apparatus. The blood introduced moves through the capillary 94 to the reagent portion 97 by capillary action and dissolves the reagent portion 97 to form a liquid phase reaction system. By the action of enzyme, the glucose in the blood is oxidized, while the electron carrier is reduced. When certain voltage is applied across the operative electrode 95 and the counterpart electrode 96 contacting the liquid phase reaction system, the reduced electron carrier is oxidized. The blood glucose level measuring apparatus detects the oxidation current and computes the glucose concentration based on the oxidation current.
A typical way to extract blood for introduction into the biosensor 90 may be to use such a lancing apparatus as disclosed in JP-A-9-266898, for example. A lancing apparatus is provided with a needle for puncturing the skin of the user to cause bleeding. By bringing the suction port 94a of the biosensor 90 into contact with the extracted blood, the user can introduce the blood into the capillary 94 through the suction port 94a. 
Recently, as disclosed in JP-A-2000-231, for example, a blood glucose level measuring apparatus with a lancing function is proposed. With it, both the lancing of the skin using a lancet (introduction of blood into the biosensor 90) and the measurement of the blood glucose level can be performed.
In using the biosensor 90 mentioned above, the introduction of blood need be performed by bringing the suction port 94a, which is very small, into proper contact with the blood. This operation necessitates the user's visual confirmation. Thus, it is an intolerable burden to introduce blood into the biosensor 90 after bleeding is caused with the use of a lancing apparatus.
In using the blood glucose level measuring apparatus having a lancing function, on the other hand, it is often difficult to visually confirm the bleeding position, which causes the following problems. The first problem is that the blood supply to the biosensor 90 cannot be repeated under the same conditions. The second problem arises when the blood supply is performed by allowing the blood to come into contact with the suction port 94a before a sufficient amount of blood has oozed out. In such a case, the time taken for introducing an amount of blood necessary for the measurement into the capillary 94 depends on the bleeding speed from the skin. Since the bleeding speed varies depending on the bleeding portion and among individuals, the time taken for introducing an amount of blood necessary for the measurement cannot be constant. Further, in the biosensor 90 utilizing the capillary system, the travel speed of the blood through the capillary 94 depends on the viscosity of the blood, which varies among individuals or depending on the physical condition. Therefore, the time taken for blood introduction into the thin capillary 94 varies largely also due to variations of the viscosity of blood.
Such variations of time for blood introduction influence the progress of the enzyme reaction, which starts by the dissolution of the reagent portion 97 in blood. As a result, reliable measurements cannot be obtained. Further, the variations of time for blood introduction often hinders the shortening of the measurement time.